Antenna construction for reducing side lobes of the radiation pattern

Abstract

A construction for reducing the side lobe energy emitted from antennas, particularly horn antennas, and thereby attenuating unwanted coupling with adjacent antennas, the construction utilizes a continuous helical coil located on the interior surface of the antenna horn in order to progressively delay the current flowing along the horn wall by causing the current to follow a longer path than that portion of the wave which propagates well away from the wall, the number of coil turns being selected to cause the portion of the E plane which arrives at the horn aperture to be out of phase by approximately one-half wave length with the portion of the E plane propagated away from the horn wall so that it will cancel the E plane energy at the aperture.

What is claimed is: 
     
       1. An antenna construction for reducing the side lobes of a radiation pattern comprising: a wave guide;   an antenna horn connected with said wave guide and having a horn wall arranged at an angle to the axis of said wave guide; said antenna radiating an energy in an E plane;   a helical coil of wire secured to the interior surface of said horn wall and having substantially the same shape as said wall;   the diameter of said wire and the number of coil turns along said horn wall being such as to delay the portion of the E plane at the aperture of said antenna horn sufficiently to make said delayed portion out of phase with the E plane portion propagated away from said horn wall.   
     
     
       2. An antenna construction as defined in claim 1 wherein; said coil is secured to said horn by fillets on each side of said wire to provide a smooth transition to said delayed portion.   
     
     
       3. An antenna construction as defined in claim 2 wherein; said helical coil provides at least six turn perturbations along said horn wall per wave length of the propagated E. plane in order to provide said smooth transition.   
     
     
       4. An antenna construction as defined in claim 3 wherein; said fillets comprise solder which is radiused from approximately the center diameter of said wire to the horn wall.   
     
     
       5. An antenna construction as defined in claim 4 wherein the diameter of said wire is determined by the formula ##EQU7## wherein `L` is the length of the horn, `λ` is the wave length, `φ` is the divergent angle of the horn wall from the axis, and "n" is the number of turns per wave length.